White Light Emitting Films from Eu(III) Complexed Copolymers of Alternating Fluorene and Bis(pyrazolyl)pyridine Derivatives

Abstract

4-Ethynyl-2,6-bis(pyrazolyl)pyridine (BPP) end-capped fluorene (FO) homo (P1) and FO-BPP main chain copolymers (P2 and P3) with Mn around 10 kDa were successfully prepared. The optical band gap of P1–P3 copolymers were 2.69, 2.88, and 2.90 eV, respectively. Spin-coated P2 and P3 thin films displayed blue and green dual emissions giving a mixed cyan color light under UV irradiation. By exploiting the metal coordinating ability of main chain tridentate BPP units, a red emitting Eu(III) ion coordinated conjugated polymer [FO-(BPP(Eu(tta)3))]n layer was formed on top of the P2 and P3 thin films via the dip-coating technique to achieve white color radiant films displaying triple emission with maxima at 425, 543, 614 nm and 428, 543, 611 nm for P2 and P3, respectively. The CIE (Commission internationale de l’Eclairage) coordinates were found to be (0.31, 0.35) and (0.31, 0.32) for white emitting films made from P2 and P3, respectively. These values are very close to the designated coordinates for a perfect white light emission (x = 0.33; y = 0.33).